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QuickGuide to Speedlite 600EX-RT 

Radio Wireless Flash Setup

 INTRODUCTION

The Speedlite 600EX-RT allows you to set up multiple Speedlites 

as “slaves” which are wirelessly controlled and synchronized by a 

“master” unit. As compared to flash units that use optical signals 

only, the 600EX-RT’s radio-based wireless E-TTL offers signifi-

cant advantages, such as the freedom to place 600EX-RT slave 

units up to 98 feet from the camera and “master unit”, all without a 

direct line-of-sight between the master and slaves. Your wireless 

radio setup options include:

 

• 

 Automatic E-TTL

 with 

equal

 output from all units

 

• 

 

Automatic Ratio E-TTL 

with 

unequal

 (ratio) output 

between firing groups

 

• 

 

 M 

– Manually-set power output (you can set a different 

flash output for each slave unit or firing group)

 

• 

 

 GR

 – Different groups have different flash modes, with 

up to five groups

Only a 600EX-RT or ST-E3-RT Speedlite Transmitter attached to 

a camera can be a master. You can, however, use two or more 

master units by setting up multiple cameras, each with a master 

unit attached, and switch from one to another during a wireless 

flash shooting session. The slave lighting setup will remain the 

same. Only 600EX-RTs can be slaves when you are shooting in 

radio control mode.

 COMPATIBILITY

EOS cameras released since 

2012

 (such as EOS-1D X, EOS 5D 

Mark III, EOS 6D, and EOS Rebel T4i) – full compatibility

EOS cameras released before 2012:

 

• 

 Flash sync speed must be one stop slower than the 

maximum

 

• 

No high-speed sync shooting

 

• 

No group (GR mode) flash 

Note:

 Full flash sync, including Hi-Speed Sync, is available with 

the 600EX-RT with all EOS SLRs when used in optical wireless 

E-TTL control mode.

 INITIAL WIRELESS RADIO FLASH SETUP

You must first set the master and slaves to matching transmission 

channels and wireless radio IDs. Once you have done so, any  

settings you make to the master will  automatically be transmit-

ted to the slaves. This eliminates the need to adjust the slaves 

individually and manually.
1.   

To set the master unit:

 Press the 

Wireless Flash Button

 until 

the RT icon (upper-right corner of the unit’s LCD screen) and 

<MASTER> 

appear. 

The wireless flash cycle via button is: Conventional on-camera 

flash > Radio-based Master unit > Radio-based Slave unit > 

Optical-based Master unit > Optical based Slave unit.

2.   

To set the slave unit(s):

 Press the 

Wireless Flash Button

 until 

the RT icon and 

<SLAVE>

 appear.

3.   

To set the transmission channel:

 Set the master and slave 

units to the same Transmission Channel, otherwise the 

slave(s) will not fire. Use the same procedure below for  

master and slave.

 

a.  Press 

Fn Button 4

 until 

<MENU 3>

 displays.

 

b.   Press the channel button (

Fn Button 1

, under the “CH” 

icon). The channel number will highlight immediately 

below RT icon. Turn the selector dial to the channel 

number of your choice (1 to 15) or AUTO. If you set 

AUTO, the 600EX-RT will automatically set the channel 

with the best reception. Set the master and slave units 

to the same Wireless Radio Channel.

 

c. 

Press 

Fn Button 4

 until 

<MENU 3>

 displays.

 

d.  Press 

Fn Button 2

 to highlight ID.

 

e.   Turn the 

Select Dial

 to the digit you want to set. There 

are four digits.

 

f. 

 Press the 

Select/Set Button

 to activate the digit setting.

 

g.   Turn the 

Select Dial 

to set any digit from 0 to 9, then 

press the

 Select/Set Button

 to register your setting.

 

h.   Repeat steps e – g to enter a four-digit number. You  

can enter any number from 0000 – 9999. The master 

and slave units must be set to same ID number. The 

number you set must be different from that of any other 

600EX-RT shooter in the vicinity.

 

i. 

 Press 

Fn Button 4

 to return the flash to shoot-ready 

mode.

 

j. 

 The

 <LINK>

 lamp should light green to indicate a 

working link between the master and slave, assuming 

both are turned on and set to same Channel/ID. 

 

• 

 If you are using more than one master, the color of the 

<LINK>

 lamp will vary depending on the order in which 

you turn the masters on. The first/main master is green. 

Subsequent/sub-masters are orange.

 

• 

 If the LINK lamp is continuously red, check to make 

sure the master and slave are set to the same channel 

and ID. 

 

• 

 If the LINK lamp is blinking red, either your setup totals 

more than 16 units or you may need to turn the power 

off and on again.

 MASTER FLASH FIRING ON/OFF

You can choose whether master flash firing is ON and therefore 

the master contributes to the flash exposure, or OFF and does 

not. The master flash will still control the slaves, regardless of 

whether it contributes to the exposure.
1.  Press 

Fn Button 4

 until Menu 2 displays.

2.   Press 

Fn Button 1

 (under Flash On/Off icon) to ON or OFF

 

a.   Three little beam lines coming from flash icon on LCD 

panel indicate Master Flash ON

 

b.   Beam icons disappear when Master Flash OFF  

is active

 WIRELESS E-TTL — “ALL” (FLASH RATIO OFF)

In this mode all flash units will fire at the same output, with full 

E-TTL auto flash exposure, which you can adjust with flash 

exposure compensation (FEC) on your camera, as necessary. 

This mode is best for lighting setups where you want even lighting 

throughout the scene. E-TTL is also great when flash-to-subject 

distances may change from shot to shot.
1.    

Perform the initial flash setup described above. 

Confirm that 

master and slave are set to the same transmission channel 

and radio ID. Position the camera and flash within correct 

operating range (30 meters/98 feet.)

2.

   Set the firing group on each slave unit. 

Set the slave unit to 

firing group A, B, or C. The slave will not fire if set to group D 

or E, when ratio control is set to ALL. You can assign multiple 

flash units to the same group.

3.   

Set the master to radio-based Wireless E-TTL.

 Press the 

<MODE> 

button on the master unit to set the master to 

E-TTL.

4.   

Set the Ratio to “ALL”

 — On master unit, press 

Fn Button 4

 

(under “Menu 1” icon) until Menu 2 appears.  

Press Fn 

Button 2

 (under “Ratio” icon) until “ALL” 

appears on master unit’s LCD panel.

5.   

Confirm wireless link.

 Confirm that the 

<LINK>

 lights on the 

600EX-RT’s are lit and green and that the AF-assist beam 

emitter on the slave is blinking at 1-second intervals. Also 

confirm that the red flash ready light is lit on the master unit. 

6. 

Shoot.

 

a.   Press the test flash button on the master flash to check 

operation. If a slave does not fire, make sure it is within 

the correct range.

 

b.   Take the picture. The flash exposure confirmation  

lamp will light for 3 secs to confirm normal exposure. 

1

2

3

Fn Button 1

Wireless

Button

Flash Ready/Test Flash

Flash Mode Button

Fn Button 2

Fn Button 3

Fn Button 4

Select Dial

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